1. Field of the Invention
The present invention relates in general to telecommunications networks. More particularly, the present invention relates to a wireless access gateway to a packet switched network and to methods for using a wireless access gateway for transmitting content to and from a mobile station via a packet switched network.
2. Description of Related Art
The Public Switched Telephone Network (PSTN) was built based on a paradigm in which functions were centered on the switch. PSTN switches typically both carry traffic, such as voice or data, and perform the signaling needed to set up connections through the network. More particularly, most switches use a Time Division Multiplex (TDM) architecture. This architecture has a number of disadvantages, however. First, the TDM architecture typically has a relatively low bandwidth and is generally optimized to carry voice traffic. Second, the current practice of reserving circuits to route calls is inefficient and requires complex traffic modeling to ensure that capacity can meet demand. Third, the control requirements and capability sets for the switches tend to vary greatly from vendor to vendor. This makes the switches difficult to update, maintain, and interwork with other network elements. Conventional switches also tend to be very expensive.
Recently, a Next Generation Network (NGN) approach has been suggested as a new approach to telecommunications network architecture. Representative of NGN suggestions are the specifications and proposals of such organizations as the Third Generation Packet Partnership Number 2 (3GPP2) and the Mobile Wireless Internet Forum (MWIF). In general, the NGN approach is based on packet switching instead of circuit switching. Moreover, in the NGN approach, the signal control logic is independent of and managed separately from the packet switching hardware. In particular, the NGN may be conceptualized as made up of a Connection Control Plane, a Call Control Plane, and a Service Plane.
The Connection Control Plane is made up of the network elements, such as the packet switching hardware, that carry the traffic, which may be voice, data, video or other media. However, unlike the switches of the PSTN, the network elements in the Connection Control Plane have little or no intelligence. Instead, a “Call Agent” or “Session Manager” in the Call Control Plane sets up and controls all the calls through the Connection Control Plane. The advantage of the separation of the Connection Control Plane from the Call Control Plane is that calls can be controlled independently of the hardware being used to carry the traffic.
The Service Plane consists of network elements, such as “Application Servers,” that provide the data and service logic needed to provide various telecommunications services. For example, when asked to route a call for a given subscriber, the Session Manager would communicate with the Application Server to determine what services may be implicated by the request and to invoke the service logic needed to provide the service.
With the rapid growth and importance of wireless networks, it is desirable to integrate wireless communication functionality into the NGN approach. However, the integration of wireless communication is more complicated, because the elements in conventional wireless networks perform many more functions than the elements in conventional wireline networks. For example, the switching elements in conventional wireless networks, mobile switching centers (MSCs), perform mobility management functions in addition to switching functions. Moreover, in code division multiple access (CDMA) networks, network elements, such as MSCs and base station controllers (BSCs) typically perform a number of physical layer functions to process the signals for transmission over the air interface. In the first of these physical layer functions, a vocoder is typically used to process voice content to provide a compressed digital voice signal. Typical vocoders used for CDMA include code-excited linear predictive (CELP) vocoders, which use a fixed coding rate. More recently, CDMA systems have begun to use vocoders based on relaxed code-excited linear predictive (RCELP) algorithms, which allow for variable rate coding. For example, enhanced variable rate codec (EVRC) technology has come to be used in CDMA systems. EVRC is described in the IS-127 specification of the Telecommunications Industries Association/Electronic Industries Association's (TIA/EIA. The IS-127 specification, which is titled “Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems” and was published on Jan. 1, 1997, is fully incorporated herein by reference.
The vocoded signal is then typically processed in various ways, such as by convolution coding, repetition, and block interleaving, to reduce errors that may be caused by transmission over the air interface. This processed signal is then typically scrambled using the user's electronic serial number (ESN). The next step is orthogonal spreading, in which an orthogonal spreading code, typically a Walsh code, is applied to the scrambled signals. The particular orthogonal spreading code defines the CDMA channel of the signal. After orthogonal spreading, each channel is then quadrature spread using a long pseudorandom noise (PN) code. After filtering, the signal is then ready to be transmitted over the air interface.
In addition, the wireless network typically performs physical layer processing of signals that it receives over the air interface. The physical layer processing of received signals is typically the reverse of the processing used to prepare signals for transmission.
Accordingly, a need exists for integrating wireless telecommunications into the NGN approach in such a way that the physical layer processing needed for CDMA communication may be accommodated.